Processes for sterilization of contact lenses are well known in the prior art. Typically such processes employ aqueous solutions of sterilants such as H.sub.2 O.sub.2 present in a concentration of 1-5 wt. %, together with adjuvants such as chelating agents (e.g. ethylenediaminetetraacetic acid), buffering agents such as alkali metal phosphates, alkali metal borates, alkali metal carbonates and mixtures thereof, etc.
After a contact time sufficient to disinfect the lens, the residual sterilant must be neutralized, i.e. converted into ophthalmologically innocuous by-products, since even traces of the sterilant remaining on the lens will result in irritation to the eye and concomitant discomfort to the contact lens wearer.
It is well known that hydrogen peroxide as a contact lens sterilant is advantageous in that it is capable of being sterilized to only water and oxygen. However such advantage is lost if neutralization is incomplete or if the neutralization agent introduces other reaction products.
Ocular exposure to 3 wt. % (the typical concentration employed for contact lens sterilization) can result in stinging tearing, hyperemia, blepharospasm, edema and possible permanent corneal damage. Indeed clinical laboratory reports have suggested that symptoms of irritation can occur at concentrations as low as 30 ppm. Clinical findings suggest that an ideal solution would be one wherein residual levels of the sterilant may be reduced to near zero concentration while avoiding introducing any spurious contaminants into the disinfecting solution after disinfection.
At the present time, there is no commercially available, approved water-soluble chlorine-based compound employed as a contact lens sterilant. This may be due to the lack of any suitable technology which will result in the neutralization of the residual sterilant to an acceptable level within a reasonable period of time (e.g. 4-8 hours) without the introduction of extraneous chemicals.
Several hydrogen peroxide-based solution have been commercialized for disinfection of contact lenses. With the exception of the platinum-based catalyst system, all other systems create by-products which can become a source of irritation to ocular tissue upon repeated usage. Such systems utilize the following reducing agents to neutralize hydrogen peroxide: